Understanding drug dependence requires understanding the factors that render drug taking preeminent among otherwise powerful reinforcers (economic, family, health and social). Discussed in this manner, drug dependence becomes an issue of choice behavior; that is, what factors result in the choice of drug over other reinforcers? Behavioral economics provides a new conceptual system to understand choice. The value of this approach is that it has developed unique concepts, methods, and terminology to quantify the effects of qualitatively different reinforcers and their interactions. This application will examine the utility of behavioral economics for understanding drug dependence. Cigarettes will function as the reinforcer in most of the proposed studies. Cigarettes were selected for two reasons: (1) cigarettes have commonalities with other drugs of dependence; (2) cigarettes can be used in studies that would otherwise raise ethical issues. Across all of the proposed studies, the focus will be the responsivity of drug self-administration to manipulations of cost (fixed - ratio value) and environmental context (presence of competing reinforcers). We will use the behavioral economic concept of elasticity to quantify these relationships. Exps. 1 and 2 will examine the effects of changes in reinforcer magnitude and deprivation on elasticity; that is, how those variables change drug consumption when the drug reinforcer is available under different FR schedules. Exps. 3 and 4 will explore the utility of behavioral economics for evaluating therapeutic interventions in laboratory analogs of treatment. Specifically, Exp. 3 will examine whether the elasticity of cigarette smoking is differentially influenced by the concurrent presence of nicotine gum vs. placebo gum. Exp. 4 will examine if the elasticity of cigarette smoking is differentially influenced by an enriched vs. impoverished environment. Exp. 5 will test the generality of the results from Exp. 4 (enriched vs. impoverished environments) to an arrangement where alcohol is the reinforcer instead of cigarettes. Exp. 6 will test whether elasticity predicts relapse to drug use; that is, subjects will participate in an intervention which will reinforce abstinence from cigarette smoking after completing a laboratory study designed to assess elasticities of cigarette consumption. We will assess the relationship between sensitivity to price in the laboratory setting and the ability of subjects to abstain from smoking in their natural environment. This study will not only examine the potential clinical utility of behavioral economics, but will also directly examine if laboratory-based findings are related to drug taking in the natural environment. Understanding the behavioral economics of drug self-administration may provide novel conceptual and empirical tools to 1) evaluate potential drug and non-drug therapies, 2) identify and study conditions that may promote or prevent drug use and relapse, and 3) measure the effects of a reinforcer (elasticity) in a way that may better indicate a drugs' dependence potential or an individuals behavioral dependence on a drug.